The present invention relates to a fluid clutch device for controlling the transmission of motive power of a vehicular engine to accessory equipment.
An example of accessory equipment driven with the engine power is an oil pump for power steering. The oil pump is belt-driven directly from the engine so that, as the engine speed increases, the pumped volume increases. The excess volume beyond a certain flow volume is discharged through a relief valve to a reservoir. Another example of the accessory equipment to be driven with the use of the engine power is a compressor for air conditioning. Conventionally, the power to the compressor is transmitted via a magnetic clutch which is activated or deactivated electrically to transmit or disconnect the engine power to or from the compressor.
Thus, in the oil pump, since the excess volume of oil is discharged through the relief valve, the engine power used to pump the excess volume is wasted. In addition, in the case of the compressor, the compressor action continues on the coolant with the revolution action of the engine, irrespective of the need for cooling, and generates needless action of the compressor particularly at high rotational speeds of the engine, resulting in waste of the engine power.
Furthermore, when the conventional magnetic clutch is activated or deactivated, a clutch armature is suddenly connected to or disconnected from a clutch pulley, so that a large noise is generated. In addition, since the accessory equipment is abruptly driven or stopped, vehicle passengers are subjected to irritating jolt upon activation or deactivation of the clutch. Furthermore, when the magnetic clutch is activated during the acceleration stage of the vehicle, the acceleration becomes blunted and the fuel consumption increases since the motive power of the engine is partly used to operate the accessory equipment.